DESCRIPTION: (Adapted from the Application) To understand fully the role of memory in high-order cognition, we must identify mechanisms involved in the reactivating (recalling) of information stored in long-term memory. While much research effort has been devoted to studying the neural mechanisms in the primate brain that hold a recent sensory event temporarily "in mind" (i.e., in what is known as "working memory"), almost nothing is known about the mechanisms that hold recalled information. Individual Project #3 will contribute to the Center's research objectives by identifying neural mechanisms involved in the recall and storage of long-term memories in the prefrontal and hippocampal system neurons. Elucidation of prefrontal and hippocampal system memory mechanisms is a major target of investigation for the Center. Monkeys are advantageous for studying memory and cognition because they can be trained to perform very complex tasks while rodents are advantageous for genetic manipulations that identify cellular mechanisms. We will test whether recalled long-term memories are maintained by the same mechanisms (and indeed the same neurons) involved in maintaining recent sensory information. This will be achieved by training monkeys to alternate between tasks that can be solved by maintaining sensory information in working memory and tasks that require recall of long-term memories. We will also examine neural activity as monkeys learn associations between stimuli that predicate the ability to recall them from long-term memory. By examining how neural activity evolves during this learning, we will be able to identify structures and mechanisms involved in forming these associations.